//
// Created by NASA on 2024/7/24.
// 线性筛/欧式筛法
//


#include <iostream>
#include <vector>

using namespace std;

int main()
{
    int n = 100; //25
//    n = 1000; //168
//    n = 10001; // 1229
    vector<bool> isp;
    vector<int> p;
    isp.push_back(false);
    isp.push_back(false);
    for (int i = 2; i <= n; ++i)
    {
        isp.push_back(true);
    }
    for (int i = 2; i <= n; ++i)
    {
        if (isp[i])
        {
            p.push_back(i);
        }
        for (int j = 0; j < p.size() && i * p[j] <= n; ++j)
        {
            isp[i * p[j]] = false;
            if (i % p[j] == 0)
            {
                break;
            }
        }
    }
    cout<<p.size();
    return 0;
}